# register
@app.route('/register', methods=['GET', 'POST'])
def register():
    if current_user.is_authenticated():
        return redirect(url_for('index'))
    else:
        if request.method == 'POST':
            if not request.form['username']:
                error = 'You have to enter a username.'
            elif len(request.form['username']) < 3 or len(request.form['username']) > 18:
                error = 'Your username must be 3 to 18 characters in length.'
            elif not request.form['firstname']:
                error = 'You have to enter your first name.'
            elif not request.form['lastname']:
                error = 'You have to enter your last name.'
            elif not request.form['email'] or \
                    '@' not in request.form['email']:
                error = 'You have to enter a valid email address.'
            elif not request.form['password']:
                error = 'You have to enter a password.'
            elif len(request.form['password']) < 4:
                error = 'Your password must be 4 or more characters in length.'
            elif request.form['password'] != request.form['confirm_password']:
                error = 'The two passwords do not match.'
            else:
                new_user = User(
                    username = request.form['username'].lower(),
                    fullname = request.form['firstname'] + ' ' + request.form['lastname'],
                    email = request.form['email'],
                    password = request.form['password'])
                db.session.add(new_user)
                db.session.commit()

                flash('You were successfully registered and can log in now.')
                return redirect(url_for('login'))
            flash(error, 'error')
    return render_template('register.html')